Process of recovering sulphuric acid from the acid-tar of benzol purification



Dec. 8, 1931. p zsc 1,835,941

PROCESS OF RECOVERING SULPHURIC ACID FROM THE ACID TAR OF BENZOL PURIFICATION Filed Sept. 7, 1927 Patented Dec. 8, 1931 UNITED. STATES.

PAUL rnrrzsorm, or RECKLINGHAUSEN, GERMANY, nss 'ononmo THE F nancier...

' STILL, 01EREGKLINGHAUSECN,GIEIRJVIANYv rnoonss or rmcovmme SULPHURIC ACID rRoMJT EncIn-tmaor snnzonf I runIFIcA'rroN" a Application flled september 7, 1927, Serial No.

The subject of this invention'is a process for the recovery of sulphuric acid used in the purification of benzol hydrocarbons and the like. s 1

The process has a fundamental property, as it takes place without the employment of any excessive quantities of diluents, such' as water or steam, and is generally characterized by the circumstance that the recovery of the sulphuric acid from the acid-tar is effected solely by mixing and stirring of the latter with a concentrated solution of ammonium sulphate. The mixture of the acid-tar .re covered from the purified benzol hydrocarbons and the ammonium sulphate solution can be effected with aid of a mixing contrivance by direct or indirect application of heat, by superheated steam for example, or entirely without extraneous. heat application. The selection of one or other of these alternatives depends upon the Working con ditions obtaining in each case, it being premised that for the attainment of a complete regeneration of the acid-tar, i. e., for complete separation'of the acid resins from the sulphuric acid which has not entered into chemical combination during the benzol purification process, the resins must keep a certain degree of viscosity. The attainment of this condition implies the maintenance of a certain temperature, say 50 to 0., in the regeneration process as a premise. In cases where larger quantities of acid-tar'are to be worked up, it will generally only be necessary at the commencement of the regeneration, during the admission of the acid-tar; into the ammonium sulphate solution, to take care that the latter possesses theabove-mentioned temperature, theheat of reaction arising during the process being sufficient for the maintenance of this temperature.

On the other hand, if only smallerquantities of acid-tar have to be worked upas is possible in the case of smaller plants-then the loss of heat in the mixing vessel will exceed the heat of reaction and will bring about an inadmissible cooling of the mixture, as, a result of which the acid resins will thicken and the separation of the sulphuric acid will be rendered diflicult. This has to be vcoun- 21s,o72, and in Germany September 20, 1926.;

teracted by a special heating of mixture, the practical method of doing thisbeing-the' application of steam-either directly vor indi-,

rectly. Wh'ereonly small quantities of heat.

are necessary, steam can be employed direct-v lywlthout hesitation, as in this casethe re.-. sultant dilution of the ammonium sulphate solutionis-negligible. Further, in thecase of a'greater degree of heat; being.required,";

it isrecommjend that indirect heat be applied in order to avoid the introduction of too m'uch, water from condensed steam into the reacting, fluids, which'wouldhave the result of unnecessarily diluting the sulphuric acid to be recovered. l '3 Whichever method is selected,-: the-acid resin separates on completion of the stirring easily and completely in the formfof 'a-vis-x cous pitch or asphalt like-mass. This floats on the liquid and,-'as it does not mix w ithr water, can easily be separated from :the acid solution. The, sulphuricv acid recovered has f been taken up by the otherwise unalter'edammonium sulphate solution. 'Onvusingqthis' solution" which has a faint red colour, for example for the manufacture. of ammonium..

' sulphate, no'furtherpitch deposit takes place,

thereby proving the theacidresini The acid resin separated out-ofthe vsolu: tion containsiall' the benzol hydrocarbons:

complete separation of v originallymixed with or dissolved in the acidtar. This being a considerable partiojf the quantity of benzol washed, itis necessary to? recover it. For this purpose the resin'after. drawing off the ammoniumsulphate-solution mustbe heatedto vaporize the benzol hydro-g carbons. The vapors are washedwith amt. kaline solution to retain small quantitiesp of sulphurous acid-and then cooled and con-f densed I f In 'orderito retain the state of fluidity of the acid resin in the'con'dition in which it exists in the acid-tar, itis desirable-to addtar, t'ar oils J or the like in the measure of 1 to 1 times, its own weight.

The process ofiers the following advane tages:- i

The process is very simple-andl'cheap in operation. It does not involve the usejof penditures of steam to remove benzol hydrocarbons from the acid resin and possibly to heat' theb'ath' at the coi'nmencementof re-" generation, no extraneous'expenses have to be applied, nor have new substances to be introduced"the ammonium sulphate solution being undiluted and in quantity as it was first introduced. I I

(2) The actual consumption of sulphuric acid-'for thepurpose of bienzol purifying, i. e., the difference between the quantity of sulphuric'acid thus employed and recovered, is-

appreciably less than that required in the .processes hitherto employed, because according tofthis invention, in the regeneration processfithe reduction from sulphuric to sel phulrou's acid which occurs quite noticeably in the-old; system, does'not take plaoeyand no noticeable quantities of sulphuric acid are carried away by the separated resin'owing to itspitchy condition.

The acid resin is recovered in a form which=greatly facilitates its further'use. It

. is practically free from acidif necessary the I last traces can be removed by washing it with water and'it can further be immediately added; to the'coal-tar to increase its pitch con tent and to improve it, or distilled and coked togetherwith coking coal in coke'ovens.

5 (4) The process can be profitably employed forthe production of sulphate of ammonia in coking installations and 5 'gas- 1 5 tree ofthe vessels: 1 and 2 on whicha trolley.

30witha lifting tackle 31mins... This. lifting. I.

works.

When working in such plants, the. am

monium'sulph'ate'solution is taken from the ammonia saturator, and, inaccordance with this invention, is "treated with acid-tan and," after the separation of the acid resin, it is returnedtogether with the recovered sulphuric aeiddissolvedth'erein directly to the ammonia saturator. It must be noticed that the sulphuric acid is in a very high degree of concentration, as it is obtained from th'e acidtar without the addition of any water.

"The process may be illustrated by meansofthe attached drawings; Fig.1 shows an elevation, partly in section; Fig'. 2 shows a cross section on the-line A-B of Fig. 1"'o f a i.- typical installation. 5 I

The mainparts of the plant are two mixing vessels 1 and *2 used for the recovering of the sulphuricacid, surround-ed by an iron frame work 3 and aworking-piatform 4, a soda lye washer 5 for washing and cleaning and a cooler6 for cooling and condensing the gases and vapors arising from the mixing vessels,

7 a run-off box 7 for the ammonium sulphate 1 Med during the process.

solution containing the sulphuric acid recov- The vessels 1 and 2 are fitted with'lids 8,

carrying a propeller 13 reachingtothe bottom of. the vessels 1 and 2 respectively. The motion of the axle 12is effected by means of a bevel gear '1 i and a: horizontahshaft o perated from platfo'rm irby means of hand winch V 15. At the bottom of the mixing vessels 1 "and 2 there are heating coils 16 in each case 'for'heat'ing by indirect steam. Through duct I 17 connected with both vesselsand discharging close under the lids in the vessels, acidtar or ammonium sulphate. solution canbe led atwi-il. TheFga'ses'and vapors developed in the vessels are drawn on by means of pipe 18'.

At the bottom of the vessels provision'has each-case been made for a run-oil 19 for the mixture ofthe ammonium sulphate solution v with the recovered sulphuric acid and 20 for the'acid resin...- The run-05 19 is connectedfby means of'trough 2'1 with a separating box 7 whereas pipe 20 discharges the acid resin into. tr'oi-i'gh 22. The vapor pipe 18 d1scharges:

into thesod'a lye washer 5 by-ineans-of a distributing hood 23. By means of pipe Qi t'he' exhaust gasesand vapors are transferred tothe cooler 6 from which'theyescape into the. 3- atmosphere through socket 25-. Cooler 6 is 4 fitted at thetop with a water ejector 32 fitted at its: lower'end with a distributinghose. The lower par of' this-cooler' serves as a separator,

thew'ater being tlrrown'oflfbv overflow-26 and i.

therecoveredbenzolthrough27L The framework 3 by meansof cross bearers I 28"carries a runway'29 arranged over the cen- To illustra tethe-working'of the process the I quantity of acid-tar produced by-the'useof 800 kg: of concentrated-.-'sulphuricv acid used in-thepnrification of ,:-.say, 1000Okg. of'crude benzol' may be workedup. This acid-tar 11:1

amounts to about 1350 kg: or 0.9 cbm; and is;

approximately of thefollowi'ng composition 1 Pure sulphuric acid (H SOQ 10' kg.

Water. (partly dilution water from original acid 'a'ndpa rtl'y' the prod not of washingreactions)'"11.1; 120 kg. Acidresins in solution; 320 l rg. Ben zol hydrocarbons"; 2O0 }kg.

After the separation of this acitl tar from the benzol it is allowed to flow into the vessels 1 or 2which have been previously filled with about 1000 flag." or 0.77 c'bm. of ammonium sulphate solutionintroduced through pipe I I 17 In cases where this solutioifcan be taken iii! from the ammonia saturator of a by-product plant,it'is drawn off from the saturator at a period when its sulphuric acid content is brought down to its lowest concentration, i. e.',

about 4%. The simplest method is to take Ammonium sulphate (NH SO; 460 kg. Sulphuric acid (H SOQ kg.

and has a temperature of about C. If

; the solution on entry is colder than this temperature, then it must be heated by means of the steam coil 16. Thereafter the heating is cut off when the requisite temperature is reached. During the process of filling with acid-tar, propeller 13 is rotated bv means of hand winch 15. As already mentioned the mixing of the acid-tar with the ammonium sulphate solution causes a slight heating of the mixture in the vessel, and this, in conjunction with the agitation generally is suificient to bring about the process of regeneration. Only in exceptional cases will it become necessary during the process of recovering the sulphuric acid to add extraneous heat with the aid of a steam coil, principally when working up smaller quantities of acid-tar, where the arising heat of reaction is not suflicient to keep the resin in a liquid state.

Any gas or vapor, including benzol vapors given off from the acid-tar during the process of filling up and mixing are drawn off through the pipe 18 and treated as below. The fluid mixture is allowed to remain in the vessel for about ten hours without heat application. The acid resin is entirely separated from the ammonium bisulphate solution, and contains the major portion of the benzol content of the acid-tar. The ammonium bisulphate solution underneath the acid resin contains about 40% free acid, and

is of pale red colour. It is allowed to run off through the bottom draw-off cock 19 of the mixing vessel and led away through run-off trough 21 and the separating box 7, eventually to the saturator. Box 7 is fitted with bafiie plates effecting a separation of any particles of resin carried away with the efliuent solution. As a' result the solution has the following approximate composition Water 500+120 620 kg.

Ammonium sulphate (NI-I 50 460 kg.- Sulphuric acid H SO pans orbox'es in which on cooling it reaches Y phate solution which ha's xpassed through the process and remains unaltered, the water been unaltered during the regeneration;- When this acid containing solution is 're-' contentof the reactingconstituents having turned to the ammonia saturator from which it was'taken, it can be used as fresh sulphuric acid with high acid content.

After drawing off the ammonium sulphate" solution the remaining resin isheated by means of coil 16 whereby the benzol hydrocarbons contained therein are volatilized and expelled." The'benzol vapors together with any other gas and steam given off are drawn through pipe 18and passed the same way as the vapors and gases alreadygiven ofl in filling and'mix-ing. The vapors and steam are first washed in the soda lye washer 5 with soda lye in'order' toneutraIiZe any small portion'of acid especially sulphurous acid gas and sulphuric-acid -which'may have'f been carried along;- After this the vapors and steam are cooled in cooler 6 by -being sprayed with water from spray 32. Gonde'm sation of the benzol hydrocarbonsandsteam takes place and separation is effected in the bottom portion of cooler 6; The spent cooling water is drawn off through'run-ofl' 26v and the benzol through run-01f 27.

The acid resin in a fluid condition freed from benzol can now be allowed. to run through the bottom run off 20 o'f'themix ing vesselalong the trough-'22 intoisuitable ordinary temperatureand becomes hard. As

previously mentioned it is ,possible,'if .required, to retain it in aliquefied state at or- I dinary temperature b adding tar or'tar oils and the likein suita le quantities to allow.

ofits being transported considerable dis tances; The admixture of these materials is effected before, during or after heatingemployed for benzol 'evaporatioiijthrough the pipe connection 10 afiixedlyto lid 8 of the mixing vessel. I [l By this admixturebf tarfnot only is a; state of fluidity of the resin maintained, but another advantage is'secur'ed, i. e.,that the 1 resin can be washed more easily with water in'the mixing vesselprior' to its discharge, tlius'removing any slight traces of acid and ammonia sulphate salt yet adhering, if. great] purity of the acid-resin isineces'sary '1 For this purpose the mixing vessels '1. and 2 with the propellers 13"canbeusedto advantage. The necessarywater for washing I is' introduced through pipe "11 in theflids" a 8 of the-vessels '1 and2. Thequantity of water required is aboutone-fift'h of'the resin tar-mixture. The wash water after separation settleson theto'p and can be easily separated from the resin-tar mixture when the' latter is drawn ofl. In order to make use of its ammonia content, it'is best mixed with" the ammonia liquor "from the by-product -plant'. l

Now, what I; claim is v 1.. The; process for treating mixing the same with a concentrated solution ot, ammonium sulphate,-whereby the sul: phuric acid contained in said tar; will enter the concentrated ammonium: sulphate solu tion, and separating and removing thezacide containing ammonium sulphate solution. a

mixing the same with a concentrated aqueous solution of ammonium sulphate, whereby the free sulphuric acid contained in said acid-tar willenter the said ammonium sulphate solu.

tiomheating-the mixture to insure rapid v stratification ofthe now acid-containing layeryand removing; the latter from thenow supernatant non-aqueoussolution of the tar.

3; Theprocess of treating the acid-tar from benzene purification, Which comprises mix-- ing. the same with a concentrated aqueous solution of acid ,a'mmoni'umsulphate whereby the free sulphuric acid contained in said "acidstar will enter the said ammonium sulphate solution, heating the mixture; toinsure rap-idstratification of the-now acid-contain ing layer, and removing the latter from the now supernatant non-aqueous solution of the miter. I r v, v

4 The process of recovering free-sulphuric the acid-tar from benzene purification, Which (1011113321889:

23. Theprocess of treating, the acid-tar from; benzene PllIlfiCZLUOII, which compmses 7.. Theprocess ofi treatingthe acidetarz of benzene purification which. comprises 'tl3.: stepszof mixing the acid-tar with asubs'tan tially 46%, aqueous solution ot'rammonium sulphate and heating. thecmixture, whereby the sulphuric: acid: contained in theacid-tar enters the ammonium sulphate solution, drawing oft the clear: aqueous solution thus formed, and heating theremaining acid-res ins, whereby the benzene and other hydrocarbons contained in the latter are vaporized;

In testimony whereof I aflix my signature;

PAUL FRITZSCHE.

acid from acid-tar derived from benzene pu- I I i rificati0n,Which comprises mixing said acidtar With a concentrated solution ofammoni- 31% um sulphate to extract the free: sulphuric acid from-said tar, wherebya supernatant. layer of a solution-of acid-resins in tar results, separating saidsupernatant layer and heating theisame to. recover volatile matter.

therefrom, and recovering sulphuric acid fromthe-lower layer of ammonium sulphate solution. 7 I

a 5,. The process of recovering freesulphuric acid from acid-tar derived from benzene pu- Irification, which comprises mixing said .acid-.

tar with an acid solution of substantially 4 6% ammoniumsulphate to. extract the free s llph-uric acidfrom saidtar, whereby a supernatant layer of a solution of acid-resins in ita rv results, separating said supernatant lay- I erandsheating the same to recover benzene therefrom, and :recovering sulphuric acid from the: lower layer of ammonium sulphate solution. v v ()Q The process of recovering sulphuric acid from'the acid-tar of benzene purification,

whi'ch comprises the st'epsof mixing-the acidtar with a concentrated aqueous solution of ammonium sulphate, whereby the sulphuric 

